1. Field of the Invention
The present invention relates to an etching method, and more particularly, to an etching method applicable to a semiconductor device fabrication and an MEMS(Micro-Electro-Mechanical System) process.
2. Background of the Related Art
In general, the etching is an essential process in fabrication of a semiconductor device as well as in fabrication of the MEMS currently under research widely, which occupy great portions of the fabrication processes. In the etching, an etching mask is always required for separate a portion to be etched from a portion to be protected from the etching. As the etching mask, a photoresist thin film, a nitride thin film, such as SiN, an oxide thin film, such as SiO2, and a metal thin film, such as Cr, can be used, selectively.
As one example, a related art wet etching will be explained. Referring to FIG. 1, in fabrication of a device having different etching depths xe2x80x98Axe2x80x99, xe2x80x98Bxe2x80x99, and xe2x80x98Cxe2x80x99, the following two methods are used in the related art.
Referring to FIG. 2A, in the first method, a first SiN etching mask layer 2 and the first photoresist layer 3 are formed in succession on the silicon substrate 1, and a portion of the first SiN etching mask layer 2 is removed by photolithography and etching, to expose a region of the silicon substrate 1. Then, as shown in FIG. 2B, the first SiN etching mask layer 2 is used as a mask in etching the silicon substrate 1 to an xe2x80x98Axe2x80x99 depth in FIG. 1, and the first SiN etching mask layer 2 and the first photoresist layer 3 are removed. Then, as shown in FIG. 2C, a second SiN etching mask layer 4 and a second photoresist layer 5 are formed in succession on an entire surface of the substrate 1, and a portion of the second SiN etching mask layer is removed by photolithography and etching, to expose a region of the silicon substrate 1. Then, as shown in FIG. 2D, the second SiN etching mask layer 4 is used as a mask in etching the silicon substrate 1 to a depth of xe2x80x98Bxe2x80x99 in FIG. 1, and the second SiN etching mask layer 4 and the second photoresist layer 5 are removed. And, as shown in FIGS. 2E and 2F, a third SiN etching mask layer 6 and a third photoresist layer 7 are used in etching to xe2x80x98Cxe2x80x99 depth in FIG. 1 in the same method as the above methods, to complete fabrication of a device having different etching depths of xe2x80x98Axe2x80x99, xe2x80x98Bxe2x80x99, and xe2x80x98Cxe2x80x99 as shown in FIG. 2G.
Referring to FIG. 3, in the second method, a first SiN etching mask layer 12 and a first photoresist layer 13 are formed on a silicon substrate 11, and portions of the first SiN etching mask layer 12 are removed by photolithography and etching, to expose regions of the silicon substrate 1 to be etched as xe2x80x98Axe2x80x99, xe2x80x98Bxe2x80x99 and xe2x80x98Cxe2x80x99 in FIG. 1. Then, as shown in FIG. 3B, the first SiN etching mask layer 12 is used as a mask in etching the exposed silicon substrate 11 in overall for the first time to a depth xe2x80x98Cxe2x80x99 in FIG. 1 which has the shallowest etching depth, and the first SiN etching mask layer 12 and the first photoresist layer 13 are removed. And, as shown in FIG. 3C, a second SiN etching mask layer 14 and a second photoresist layer 15 are formed in succession on an entire surface of the substrate 11, and a portion of the second SiN mask layer 14 is removed by photolithography, to expose the silicon substrate 11 only in the xe2x80x98Bxe2x80x99 region of FIG. 1. Then, as shown in FIG. 3D, the second SiN etching mask layer 14 is used as a mask in etching the silicon substrate 11 etched for the first time for the second time, and the second SiN etching mask layer 14 and the second photoresist layer 15 are removed. And, as shown in FIGS. 3E and 3F, a third SiN mask layer 16 and a third photoresist layer 17 are used in etching xe2x80x98Axe2x80x99 region in FIG. 1 etched for the first time for the second time by a method the same as the foregoing method, to complete fabrication of a device having different etching depths of xe2x80x98Axe2x80x99, xe2x80x98Bxe2x80x99 and xe2x80x98Cxe2x80x99 as shown in FIG. 3G.
However, the related art methods are complicated since photolithography and etching mask removal are required every time xe2x80x98Axe2x80x99, xe2x80x98Bxe2x80x99 and xe2x80x98Cxe2x80x99 regions are etched. And, an etching mask used in a prior etching should be removed before a following etching process is started, and if the etching mask is not removed perfectly, formation of an etching mask for the following etching can not be done properly. That is, in the removal of the etching mask used in the prior etching, if the etching mask is not removed properly after the prior etching process is finished, there are over-hangs of the etching mask left at edges of the etched regions as shown in FIG. 4, which causes a shadow effect in formation of an etching mask for the following etching, to impede formation of an etching mask thin film at the edges of the etched regions. And, as shown in FIG. 5B, in the photolithography, misalignment of a mask pattern is occurred, which impedes fabrication of a precise device, particularly, as shown in FIG. 5A, in an MEMS fabrication, in order to enhance a device precision, an improvement of an etching process that can reduce an alignment error of the mask pattern is required.
Accordingly, the present invention is directed to an etching method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an etching method which can reduce a misalignment error of a mask pattern in etching.
Other object of the present invention is to provide a simple etching method which permits to etch to a variety of depths by using only one etching mask.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the etching method for forming a plurality of trenches or recesses having depths different from one another in a substrate, includes the steps of forming an etching mask on the substrate, forming a plurality of patterns in the etching mask corresponding to depths of the plurality of trenches, and etching the substrate using the etching mask having the plurality of patterns formed therein.
In other aspect of the present invention, there is provided an etching method, including the steps of forming an etching mask on a substrate, etching a first, a second, and a third regions in the etching mask to a first depth on the same time, forming a first mask pattern in the first region, and using the first mask pattern as a mask in etching the second and third regions of the etching mask on the same time to a second depth, removing the first mask pattern, and forming second mask patterns in the first and second regions, etching the third region of the etching mask using the second mask patterns as a mask, to expose the substrate, removing the second mask patterns, and using the etching mask as a mask in etching the exposed substrate to a third depth, etching the second region of the etching mask to expose the substrate, and etching the exposed substrate to a fourth depth using the etching mask, and etching the first region of the etching mask to expose the substrate, and using the etching mask as a mask in etching the exposed substrate to a fifth depth.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.